Treating earthenware bodies

ABSTRACT

A method of treating earthenware bodies to enhance resistance to freezing and to assist the application of decals and the like thereto comprises treating the bodies with a liquid medium containing a water-repellent material such as silicone. In a subsequent drying step, the bulk of the liquid medium is removed while leaving the water-repellent material deposited in the pores of the earthenware body. In this way, subsequent entry of water and freezing and cracking is resisted. It has also been discovered that the treatment also enchances the ability of the earthenware surface to receive decals and the like without the need for glazing and an additional firing step.

BACKGROUND OF THE INVENTION

This invention relates to the treatment of the ceramic and otherearthenware bodies, and is particularly but not exclusively concernedwith the treatment of fired clay bodies in the form of ceramic garden orpatio pots. Other applications include hanging pots, wall hangers, housebricks and ceramic roof tiles, or any other ceramic, fired clay orearthenware article.

One particular problem associated with ceramic pots and containersintended for use outdoors eg in gardens, patios and on walls, is thetendency towards damage due to the action of frost. It is a well-knownfact that when water is absorbed into the walls of porous earthenwarepots, freezing temperatures will case that water to expand and the potswill often crack, laminate, effloresce or simply fracture.

Attempts have been made in the past to obviate this problem by makingsurfaces of the pot water repellent or waterproof, eg by glazing. If theglaze is applied while there is still some moisture in the earthenwarethen freezing temperatures will nevertheless have the same detrimentaleffect on the ware. Further, it has been found that because of theenvironment in which garden or patio pots are used and located, damageis often suffered by; the glaze, allowing ingress of water or moisturewhich is acted upon by the freezing temperature so that expensive andattractive pots are damaged and often destroyed.

Some earthenware pots are decorated by decalcomania transfers or by handpainting, the decoration being then fired onto the surface. It ispreferred that the surface area of the pot where the transfer or paintis to be applied is smooth and for this reason the surface is sometimesglazed before applying the transfer or other art work. This processinvolves an additional firing which adds to the cost of the decoratedware.

It is an object of the invention to provide a method of treating ceramicor other earthen ware that does not suffer from some or all of the abovedisadvantages and which results in a pot which reduces the damage byreason of freezing temperatures acting on the ware, and/or to provideimprovements generally.

A further alternative object is to attempt to provide a method oftreating earthen ware and the like to enable it to be more receptive todecals or other decoration without the need for glazing the ware beforedecorating it.

A further alternative object includes attempting to provide ceramic orother earthen ware which does not suffer from the known limitations andfaults of ware produced by conventional processes.

SUMMARY OF THE INVENTION

According to the present invention there is provided a process ofimpregnating a fired earthenware body and a product made by thatprocess, as claimed in the accompanying claims.

In one embodiment, a method of treating a fired earthenware bodycomprises treating the body with a liquid medium comprising awater-repellent constituent such as silicone, drying the body so as toleave the water-repellent constituent within the pores of the body,whereby resistance to entry of water and subsequent freezing isimproved.

In the embodiment, the step of drying the body is preferably carried outat a raised temperature below 200° C., whereby the rate of drying isincreased, but degredation of the silicone or other water-repellentmaterial is minimized. In the embodiment, pressure may be applied tocause the water-repellent medium to more thoroughly permeate the porousstructure of the earthenware.

In another embodiment, an earthenware body is provided with enhancedability to receive a decal or transfer or other decorative element bytreatment with a liquid medium such as a silicone-containing liquidmedium (in the form of a solution in a solvent, or a dispersion oremulsion in water, for example). In this way, it has been found,surprisingly, that the necessity for the provision of a glazed surfacefor the satisfactory application of decals and the like is avoided.Surprisingly, after treatment with a silicone-containing liquid medium,and subsequent drying, decals can be applied. In a subsequent firingstep, in which the temperature is raised above 200° C., the siliconematerial is removed, while the transfer remains and thus significantadvantages are provided over previous techniques in this field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view through a drying or other treatment ovencontaining an earthenware pot in part of the processing operation;

FIG. 1a is an enlarged section of part of the pot seen in FIG. 1;

FIG. 2 is a section view of an impregnation tank containing a pot in afurther part of the process;

FIG. 2a is an enlarged section view of part of the pot seen in FIG. 2;

FIG. 3 is a view similar to FIG. 2 in a further part of the process;

FIG. 3a is an enlarged section view of part of the pot seen in FIG. 3;

FIG. 4 is a section of a drying apparatus;

FIG. 4a is an enlarged section view of part of the pot seen in FIG. 4;

FIGS. 5a, 5b, 5c, 5d and 5e are part sections through the wall of a potduring a process for decorating the fired clay pot.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As seen in FIG. 1 an earthenware pot P, having side walls W is locatedwithin a drying oven 2 and any moisture present within the pot is causedto evacuate.

After cooling, the totally dried out pot is then placed within a tank 4containing a silicone water solution S which then impregnates the pothydrostatically. To expedite the impregnation process a lid 6 issealingly fitted over the top of the tank and compressed air is fedthrough a port 8 to pressurize the tank as seen in FIG. 2. The tankremains in this condition for a pre-determined period of time accordingto the size and thickness of the pot or pots placed therein, when theearthenware is totally impregnated by the silicone solution S_(S). Ifdesired, the silicone solution may include any other vehicle besideswater, eg a solvent. In this specification, unless otherwise stated,references to a "silicone solution" in water are intended to refer to asolution or dispersion or emulsion of a silicone compound in water, forexample an aqueous solution of potassium methyl siliconate.

The tank is then depressurized and the solution is drained away via adrain cock 10 as seen in FIG. 3. The silicon impregnated wall of the potis shown in FIGS. 2a and 3a.

The next step in the process is to remove the moisture from the siliconesolution S_(S). To this end, the pot is placed within a kiln 14 andsubjected to a temperature of between 100° centigrade and 150°centigrade. This drives the remaining moisture out of the pot in theform of water vapor. Alternatively removal of the moisture content maybe effected by subjecting the ware to a vacuum, eg by sealing the warein a tank and then connecting to a vacuum source or the body may beexposed, after impregnation to a carbon dioxide atmosphere.

The earthenware pot is thus fully impregnated with water resistantsilicone crystals S_(S) as illustrated in FIG. 5a, which is found to beeffective in preventing any moisture being absorbed by the first claypot and therefore is immune from frost damage.

It is frequently desired to decorate earthenware pots by the applicationof a decal transfer or by hand-painting or spraying.

It is found to be beneficial for the transfer or other decorating mediumto be applied over an area of the pot or other ware which has beenimpregnated by a silicone mixture after which the transfer is "fired on"to the ware in the usual manner. Such a preparatory process enableslight-fast and waterproof colors to be applied resulting in vividlong-life decorations on the earthenware body.

"Fired on" color is also found to provide the effect of fine lines anddetail, giving greater definition on waterproofed ceramic bodies than onporous fired clay bodies.

In this process an earthenware pot is dried thoroughly in a drying ovenafter which the area of the pot to be decorated has applied thereto thesilicone based water repellent solution, by painting by brush, byspraying, or by total immersion of the pot in the solution.

The pot with its applied solution is next allowed to thoroughly dryafter which the art work or decoration eg decal transfer, brush or spraypainting, rubber gelatine or silicone stamping, screen printing, montageor thermoplastics technique is applied in the usual manner. The transferor other decoration is then "fused on" to the pot by subjecting it tokiln firing at a temperature between 700° C. and 800° C. During thisfiring, when the temperature has exceeded 200° C. the silicone baseburns away without disturbing the transfer, leaving a totally porouspot. Impregnation of the pot with a liquid silicone solution can then beapplied as described earlier if so desired.

The above decorating process is illustrated in FIGS. 5a, 5b, 5c, 5d and5e.

FIG. 5a illustrates part section of the wall of an earthenware potshowing a small section of the pot being impregnated on the outersurface by a brushed on solution S_(S) of silicon. FIG. 5b illustratesthe wall of the pot after it has been subjected to a drying operationwhereby the outer surface of the wall comprises an internal "skin" ofsilicone crystals Sc. FIG. 5c illustrates the application of a transferT to the outer surface of the wall of the pot and FIG. 5d illustratesthe decorative element having been "fused on" into the wall of the pot.FIG. 5e illustrates the final resultant wall of the pot after thesilicone solution has been impregnated into the pot and the moisturecontent of the solution has been evacuated leaving the waterproofingsilicone crystals Sc within the clay body.

In a further process a backing of light colored paint or a light coloreddecal transfer, may be applied to the ware after the initialimpregnation of silicone, in order that the colors of the transfer maybe more outstanding.

In some circumstances it is beneficial to impregnate the ware with asilicone solution which contains a coloring medium and the ware wouldthen be colors where impregnation takes place. The ware need not beimpregnated by colors silicone solution over its entire area, onlyselected bands or other areas being so treated. One method of effectingthis is to impregnate the area where coloring is not required withcolorless silicone solution. The coloured silicone solution is thenapplied by brushing, spraying or immersion, the colorless solutionacting as a mask to prevent color passing on to the plain areas.

Although the process of the invention has been described with referenceto an earthenware pot, it should be understood that it can be used inthe treatment of other fired clay products, eg house bricks, roof tiles,and un-glazed floor tiles.

What is claimed is:
 1. A process for making a decorated earthenware bodycomprising:a) providing said earthenware body which is porous; b)impregnating at least a portion of said earthenware body with a siliconebased water repellent solution thereby providing an area receptive tothe application of a surface decoration thereto; c) drying saidearthenware body below 200° C.; d) applying said surface decoration tothe portion of said earthenware body impregnated with said siliconebased water repellent solution; and e) heating said earthenware body toa temperature in excess of 200° C. to remove said silicone based waterrepellent solution leaving said surface decoration on said earthenwarebody intact.
 2. A process according to claim 1, further comprising thestep of applying an underbody or a coating of paint or a decal to anarea of said earthenware body where said surface decoration is to beapplied.
 3. A process according to claim 2, wherein said silicone basedwater repellent solution comprises potassium methyl siliconate.
 4. Aprocess according to claim 1, wherein said temperature is in the rangeof 600° C. to 1500° C.
 5. A process according to claim 1, wherein saidsilicone based water repellent solution comprises potassium methylsiliconate.
 6. A process according to claim 1, wherein said siliconebased water repellent solution comprises a coloring medium.
 7. A processaccording to claim 6, further comprising the step of reheating the bodyto a temperature of less than 200° C.